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Global Change Master Directory (GCMD) Keywords

Global Change Master Directory (GCMD) Keywords are a hierarchical set of controlled Earth Science vocabularies that help ensure Earth science data, services, and variables are described in a consistent and comprehensive manner and allow for the precise searching of metadata and subsequent retrieval of data, services, and variables. Initiated over twenty years ago, GCMD Keywords are periodically analyzed for relevancy and will continue to be refined and expanded in response to user needs.
The categories of GCMD Keywords are as follows.

Earth Science

Earth Science Services

Data Centers/Service Providers

Projects

Instruments/Sensors

Platforms/Sources

Locations

Horizontal Data Resolution

Vertical Data Resolution

Temporal Data Resolution

URL Content Types

Granule Data Formats

Measurement Names

Chronostratigraphic Units

The information provided on this page defines how GCMD Keywords are structured, used and accessed. It also provides information on how users can participate in the further development of the keywords.

GCMD Keyword Community Forum

The GCMD Keyword Community Forum provides keyword users and metadata providers with an area for discussion of topics related to GCMD Keywords. Participants are invited to use this forum to ask questions, submit keyword requests, discuss trade-offs, and track the status of keyword requests.

More Information About the Keywords

GCMD Keyword Structure

GCMD Keyword Structure

GCMD Keywords are organized using a multi-level hierarchical structure. This hierarchical structure provides a framework by which concepts can be classified and related. The Earth Science and Science Services keyword sets use the following hierarchical structure:

Category > Topic > Term > Variable > Detailed Variable

Categories and Topics represent disciplines and high level concepts. Terms and Variables define subject areas and parameters. Detailed Variables are uncontrolled values that can be added by users to more specifically describe data.

All other keyword sets use hierarchies designed for a specific concept. For example, "Instruments" uses Short Name > Long Name. Short name and long name define the name of the instrument used to acquire the data.

Earth Science Keywords Structure

The Earth Science Keywords
have a six-level keyword structure with the option for a seventh uncontrolled field. Category and Topic levels define how the keywords are organized and the associated Earth science discipline within the hierarchy. The Term and Variables levels define the subject area, measured variables/parameters, and the hierarchical-type relationship for the subject area.

Keyword Level

Example

Category

Earth Science

Topic

Atmosphere

Term

Weather Events

Variable Level 1

Subtropical
Cyclones

Variable Level 2

Subtropical
Depression

Variable Level 3

Subtropical
Depression Track

Detailed Variable

(Uncontrolled Keyword)

Earth Science Services Keywords Structure

The Earth Science Services Keywords have a four-level keyword structure with the option for a fifth uncontrolled field. Category and Topic levels define how the controlled keywords are organized and the associated Earth Science Services discipline associated with the keyword in the hierarchy. The Term and Variable levels define the subject area, the type of software/service being described, and the hierarchical-type relationship for the subject area.

Keyword Level

Example

Service Category

Earth Science Services

Service Topic

Data Analysis and Visualization

Service Term

Geographic Information Systems

Service Variable

Web-Based Geographic Information Systems

Detailed Variable

(Uncontrolled Keyword)

Data Center/Service Provider Keywords Structure

The Data Center/Service Provider Keywords have a short name and long name that define the data center, service provider, organization, or institution responsible for distributing the data or developing the service.

Keyword Level

Example

Short Name

LP DAAC

Long Name

Land Processes Distributed Active Archive Center

Project Keyword Structure

The Project Keywords have a short name and long name that define the name of the scientific program, field campaign, or project from which the data were collected.

Keyword Level

Example

Short Name

ESIP

Long Name

Earth Science Information Partners

Instrument/Sensor Keyword Structure

The Instrument/Sensor Keywords have a short name and long name that define the name of the instrument used to acquire the data.

Keyword Level

Example

Short Name

MODIS

Long Name

Moderate-Resolution Imaging Spectroradiometer

Platform/Source Keyword Structure

The Platform/Source Keywords have a short name and long name that define the name of the platform used to acquire the data.

Keyword Level

Example

Short Name

Aqua

Long Name

Earth Observing System, Aqua

Location Keyword Structure

The Location Keywords have a five-level keyword structure with the option for a sixth uncontrolled field and define the name of a place on Earth, a location within Earth, a vertical location, or a location outside of the Earth.

Keyword Level

Example

Location Category

Continent

Location Type

North America

Location Subregion 1

United States of America

Location Subregion 2

Maryland

Location Subregion 3

Baltimore

Detailed Location

(Uncontrolled Keyword)

Horizontal Data Resolution Keyword Structure

The Horizontal Data Resolution Keywords have a range structure and define the horizontal resolution of the data.

Keyword Level

Example

Resolution Range

1 km - < 10 km

Vertical Data Resolution Keyword Structure

The Vertical Data Resolution Keywords have a range structure and define the vertical resolution of the data.

Keyword Level

Example

Resolution Range

1 km - < 10 km

Temporal Data Resolution Keyword Structure

The Temporal Data Resolution Keywords have a range structure and define the vertical resolution of the data.

Keyword Level

Example

Resolution Range

1 minute - < 1 hour

URL Content Type Keyword Structure

The URL Content Type Keywords have a type-subtype structure and define the type of URL being referenced.

Keyword Level

Example

Type

Get Data

Sub-Type

Earthdata Search

Granule Data Formats Keyword Structure

The Granule Data Formats Keywords have a one-level keyword structure and represent the format of the data that is distributed by the data center.

Keyword Level

Example

Granule_Data_Format

GRIB

Measurement Names Keyword Structure

The Measurement Names Keywords have a three-level keyword structure and define an observable property, usually geophysical, geo-biophysical, physical, or chemical.

Keyword Level

Example

Context_Medium

atmosphere

Object

air

Quantity

pressure_anomaly

Chronostratigraphic Units Types Keyword Structure

The Chronostratigraphic Keywords have a five-level keyword structure and define the geologic time of the data.

Community Use of GCMD Keywords

Community Use of GCMD Keywords

NASA’s Earth Observing System Data and Information System (EOSDIS) as well as numerous other U.S. and international agencies, research universities, and scientific institutions use GCMD Keywords as an authoritative vocabulary, taxonomy, or thesaurus to describe Earth science data, services, and visualizations. Many of these organizations also use GCMD Keywords to create ontologies for the Semantic Web, and to search and access Earth science data within online metadata catalogues. A representative list of organizations using GCMD Keywords is shown below.

GCMD Keyword Governance and Community Guide Document

GCMD Keyword Governance and Community Guide Document

The GCMD Keyword Governance and Community Guide Document, Version 1.0, is intended to provide the community with a comprehensive resource that describes the governance structures and process for reviewing proposed changes to GCMD Keywords. The document includes an overview of the structure of the keywords, requirements and recommendations to consider when requesting keyword changes, and instructions for submitting change requests. The process described in this document will be the basis of all future GCMD Keyword reviews. The community is invited to provide feedback.

The Change Process Overview diagram conveys the end to end process of a keyword including initial request, triage, approval, notification, and implementation.